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OT: pulling a vacuum in 5 gal buckets

10-17-2012, 12:06 AM

I can find many hand pumps for pulling a vacuum in a plastic sack, vacuum seal bags or in glass jars, but nothing that looks practical for 5 gallon buckets. The larger ones look like they are going to get into the 3 digit dollar range, which is not good at this time. The buckets are full of things like grains, cloth items, light tools and such. What I want is enough vacuum to firmly seal the snap-on lid down on the gasket.

I don't have the valve figured out, yet, but I think a flap valve style thingy would be fabricated fairly easily. Or, perhaps a standard tire valve, since I don't need a full vacuum, just some reverse pressure.

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Or just heat the contents and bucket to about 200 degrees then put the top on. When it cools, it will be under vacuum. So much so, that you'll probably have to punch a hole in the top to open it. The bucket will handle the heat but you have to watch the contents. You probably wouldn't even need to go that high of a temperature. Maybe 50% over ambient.

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I experimented once with surgical tubing and air pressure. Apply pressure, and at a certain point, the tubing suddenly goes from swelling slightly to a much larger diameter. If you mounted it within a cylinder that has that same inner size and shape, the first expansion will drive out all the air inside the cylinder. Then as you remove the air pressure, the tubing will collapse and draw a vacuum in the cylinder. With suitable in and out valves, and a suitable valve to control the air, you could generate a vacuum.

In practice, you would keep the size of the cylinder enclosing the section of surgical tubing to something smaller than the expanded size of the tubing. That way it would probably last quite some time, plus having a smaller final diameter it will have more 'pull' when contracting.

This is a way of getting a pretty good vacuum by using your compressed air system. Probably not super efficient, but very compact and no rings to leak, oil to fill, etc. In and out valves could be simple- the main item would be the pressure side valve to alternately pump, then release, pump, release, etc.

I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my pass​ion-

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Plastic pails with sealable lids don't do vacuum very well. The polypropylene wants to yield and will in hot weather relieving the internal vacuum to a certain extent.

Oxygen and light is the enemy for long storage items, particularly food. Why not a nitrogen purge? Set a small container of LN2 in the bottom of the pail, fill it with your goods and a dessicant bag, and place the lid (which with a brick on it to make a very low pressure check valve) without sealing it. After a time the LN2 will evaporate diffusing through the contents, sweeping up the air and O2 ahead of it. and escaping the lid. After a few hours seal the pail and you're done.

Use a food grade black pail and you will be certain of no funny smells or flavors and no light degradation. When properly sealed they are DOA certified to seal tight for food containment.

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The pail will fold/crease/dent in on itself over time. I forget for what (I think bleeding brakes or sucking oil out of a crankcase) but I tried pulling a vacuum in a pail before, it started to work then I had a mess on the floor.

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I agree with Forest, but also would speculate a little further that vacuum packing for anything but metal cans and mason jars could be problematic.

At work we are dealing with sealing an electronics cavity in a part that lives in a wet environment with wide temperature changes. The part involves metal terminals and other components passing through glass-filled nylon overmolding. Hermetic? Not so, even though the nylon is in intimate contact with the metal parts.

I relate this only to illustrate that maintaining a pressure equilibrium between inside and outside has a better chance of preventing infiltration of undesireable substances. In preservation, removal of the oxygen and prevention of its return is the goal. Secondary but also important, is the prevention of infiltration of unwanted chemicals, bacteria or mold spores.

A sustained vacuum in all but the most impermeable container is working full time at trying to suck in air, moisture and opportunistic contaminants. The two mechanisms working to force air in (and out) are variations in temperature and barometric pressure. Not much can be done about the latter, so the the usual advise about storage in a temperature-stable environment is about the best that can be done.

Back to my problem with the water infiltration on the part I described: I have suggested a diaphragm be incorporated into the design, allowing the pressure inside the cavity to remain equal with the outside, the diaphragm flexing with the pressure variations. This would prevent the moisture from being sucked in when the hot part and the air inside the cavity is suddenly cooled by a splash of water. So far, the proposal has been rejected. Perhaps I will have to build a working proof-of-concept to convince the doubters. Or disabuse myself of the notion that it is possible...

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The buckets are full of things like grains, cloth items, light tools and such.

Ah I see we have some interests in common. Word to wise is you can't pull a vacuum on those things. O2 permeable. Ruins the buckling strength of the buckets so you can't stack them anymore, or even worse they collapse randomly in the future. Pitifully weak under negative pressure. Seal usually not designed to hold anyway. Also a partial vacuum will NOT prevent insect eggs and mold from growing in the grain. So you need to purge the air with pure nitrogen, or welding argon, or CO2 from dry ice. Propane or helium could technically work but are really dumb ideas.

Supposedly the best way to do it is to stick a hose to the bottom of a mylar (O2 impermeable) bag, fill with grain, wait until the "air" coming out of the bag blows out a candle, then blow a little more in, then Finally "vacuum" pack which firms up the bag, takes up less space, and makes it visually obvious there's no hole in the bag, and sucks any remaining air out. Mylar bags are NOT rodent proof, but 5 gal buckets more or less are rodent resistant. Own a cat (or let a cat own you, as seems the case with felines)

Its not entirely unusual to spend more money on mylar / O2 packs than on the grain.

Also before you store your "tools" check for oil/grease compatibility. Some cleaning solvents etc will weaken the plastic. If it cannot be shipped in bulk in a 5 gal plastic bucket, I would not apply it to "tools" and then seal them in a plastic bucket, the mfgr knows something... You can buy 5 gallons of WD-40, shipped in a STEEL container... that says something.

Never store anything but food in a food container. Mylar or no, theoretically impossible yeah blah blah, regardless of all the arguments if you store "tools" in a bucket with grains, the grain is going to eventually taste like cosmoline.

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At work we are dealing with sealing an electronics cavity in a part that lives in a wet environment with wide temperature changes. The part involves metal terminals and other components passing through glass-filled nylon overmolding.

Oil immersion? A guy I know did that with wifi gear. Note that "all" electronics are distilled water/ethanol compatible because that's how the flux is washed off, but only some plastics are mineral oil compatible, not unusual for the plastic sleeve to dissolve off electrolytic caps, or the ink to literally wash off and deposit elsewhere. If you're doing RF stuff this will mess with the dielectric constant but then again it might all work anyway. If you're doing power stuff try to pick an oil that won't burn, there was this amazing polychlorinated biphenol compound but it turned out to have serious other issues.

Water will accumulate under the oil. It might take decades to fill 6 inches of slop space.

You can't keep liquid off rough environment stuff. However, you can pick the liquid and almost anything is better than water.